New 12v battery

Discussion in 'Prius c Care, Maintenance and Troubleshooting' started by actiondonkey, Dec 5, 2014.

  1. actiondonkey

    actiondonkey Member

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    So I'd been having a problem with the 12v battery not holding enough charge to start the car if it's not run every 2 days or so. After looking around online I found a few other owners had the same problem as it seems the OEM battery is very sensitive to complete drains. Also adding to the problem is I've installed a BMF sound system and headrest monitors which, when the car runs a disproportional amount in EV mode during in-town commutes, puts extra strain on the 12v as the alternator isn't running to provide charge.

    Eh, whatever, right? I'm still getting 70mpgs in town. But as a result I needed to purchase a new 12v and my dealership wanted about $240 for a new one -- my jaw almost hit the floor. Talk about price gouging for a really crappy battery! As such I was determined to find an aftermarket alternative just to show those F'ers whose boss around here! Little did I know the hassle that would ensue and how rare and 'proprietary' these Prius 12v batteries are. Seems the form factor is really at issue here as the OEM battery, as well as it's tiny cubby under the passenger seat, is quite small and has limited headroom. Adding to the problem is one of the battery posts is not standard size; it's about half the diameter of a standard battery post.

    After spending a good hour calling local (FL) auto part shops and even taking the battery in to try and match it; I found only one at O'reilly Auto - some BS generic brand called SuperStart and they still wanted $190. At this point I'm thinking FML I know I should have used a capacitor on this amp and I'll just cut off that stupid narrow battery connector, put on a full-sized one, and then buy a reasonably priced battery with similar specs to the OEM. Perhaps that still was the most economical option, but at last, I found a great battery that fits perfectly.

    It's the Optima YellowTop S46B24R. Yeah, I still took one in the butt on the price - $186.04 OTD after core refund - but I needed it immediately due to an upcoming road trip and the specs are superior the the OEM and SuperStart options. The engine even starts more smoothly than it ever did with the OEM. Plus it looks kvlt as all get-out so you can impress your hybrid friends with an awesome looking battery if you ride around with the seat shield off (not recommended) like those of us who've had to charge up every two days. So, in closing, if you also find your OEM battery is unable to handle extreme pulls from A/V equipment for which it wasn't intended to be used with in the first place, or if the OEM battery really is just a piece of $hit, try out the Optima. And a little nugget for the folks who read this POS post to the end - buy from Advance Auto and search online for a discount/coupon code - you'll get an extra $50 off the purchase. Or check Amazon and they go for $130-$150
     
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  2. ftl

    ftl Explicator

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    Whatever the problem is with your 12V battery, it isn't caused by running in EV mode. The Prius has no alternator, and the 12V battery is charged from the traction battery whenever it needs it, regardless of whether the engine is running or not. As long as the car is in Ready mode, even when parked, the 12V battery can charge. What does kill the 12V battery is using it in Accessory mode for more than a few minutes.

    There have been mixed reviews here recently on the Optima YellowTop batteries, with some members reporting batteries received partially discharged, and others finding relatively short lives on new batteries. A search will pull up many threads.
     
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  3. GregP507

    GregP507 Senior Member

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    If that fails, try 9 EverReady "D" cells in a cardboard tube.
     
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  4. Yakoma

    Yakoma Active Member

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    I have a Gen II, not at a C (so it might not be apples-to-apples), but I recently found the OEM battery at a metro ATL dealer for $160 + tax. They had a Black Friday special for 20% off parts & service during Service, but I persuaded them to give me the discount for parts from the Parts desk. Second choice would have been Optima from Amazon, but I got a little antsy given some of the feedback on the board here.
     
    #4 Yakoma, Dec 5, 2014
    Last edited: Dec 5, 2014
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  5. bisco

    bisco cookie crumbler

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    could it be the audio system?
     
  6. Yakoma

    Yakoma Active Member

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  7. Andyprius1

    Andyprius1 Senior Member

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    Obviously. As I said in another thread, I ran my battery down to. "no start,blank screen, no lights. And then just jumpered it with a 12V I keep in the Garage. And no more problems. I have done this FIVE times with the C and each time = full recovery. Why 5 times, I keep leaving the keys in the ignition, and Off. My other car is a PIP. I am amazed how good the battery recovers // does it really not run down ??
     
  8. bisco

    bisco cookie crumbler

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    maybe they put a limiter on it?
     
  9. Andyprius1

    Andyprius1 Senior Member

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    . Yes, it's very possible they did something........useful......finally............on the 12V

    It would be nice if Toyota communicated.
     
  10. bisco

    bisco cookie crumbler

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    we can only dream...
     
  11. Easy Rider 2

    Easy Rider 2 Senior Member

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    First, your car does not have a conventional alternator. The battery is charged from the main HV battery any time the car is in RUN mode.

    Second, a lot of owners have found the replacement OEM battery to be of good quality and respectable life. Using IT would not have cost you THAT much extra and would have saved a LOT of time. In addition, several others have reported problems with short life of the Yellow Top that you ended up getting.

    And finally, new batteries need to be fully charged at the beginning. If you haven't done that already, it is not too late.
    Also the charging voltage should be checked.......just incase your extra load has messed up the DC/DC converter that actually does the charging.
     
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  12. actiondonkey

    actiondonkey Member

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    Thanks FTL for info about the lack of an alternator. Guess we can count that one out unless it just doesn't recharge the 12v at the rate of a 'normal' car/truck. Bisco it could be the audio is putting more draw on the battery than the traction could recharge and it was only partially charged for a while, thus reducing it's mtbf. Makes sense. Thanks for the feedback, I did a top-off charge on the yellowtop and so far so good.
     
  13. GregP507

    GregP507 Senior Member

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    I already made my rant about Optima, but suffice to say, beware of those companies which have been bought out by their competitors with a goal towards removing the competition.
     
  14. Andyprius1

    Andyprius1 Senior Member

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    You could put a Ammeter in series with the 12V battery and read the current draw, normal state, in accessory, and finally in ready. Compare the three currents, especially with your sound system ON. Compare the three readings. In accessory mode w/ the amplifier on, it may be pulling too many amps. In ready it may be OK.
    In Generation 2, we had a few people run thier battery down just listening to the radio. While parked!
     
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  15. GregP507

    GregP507 Senior Member

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    It's possible, but rare for the stereo to work while drawing excess current. Usually this will make a component fail, or get very hot, in which case you would probably smell something wrong.

    It's very unlikely that anything could draw enough power to exceed the capacity of the DC converter, in which case it would trip a breaker. Its remotely possible it could be that the converter is failing, but that's unlikely without a warning.

    My 12V aux battery was bad when I took delivery of my vehicle. It went dead after barely 10 minutes in acc-mode. The dealer tested it and found it faulty, and replaced it. Since then, I don't use acc-mode. It's much easier to just put the car in ready-mode. The battery never goes dead that way, and the engine runs very little, but it does when needed.
     
    #15 GregP507, Dec 8, 2014
    Last edited: Dec 8, 2014
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  16. actiondonkey

    actiondonkey Member

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    Almost all of the times my OEM battery was completely drained was when my kid(s) left a headrest monitor on. I have them hard-wired to the battery with an interrupter in between. I've been meaning to run that power from that ATT port on the amplifier or some other source easily accessible and only powered during operation.

    On another note, I think the first couple times my recharger was on the mode for a generic 12v battery and not AGM. I suppose that could make a difference also.
     
  17. Easy Rider 2

    Easy Rider 2 Senior Member

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    In the context of this discussion, "excessive current" means more than the 12 V charging system and battery can safely supply.
    The assumption is that the new stereo is designed to pull that much current.
     
  18. GregP507

    GregP507 Senior Member

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    In this sense, I meant that the stereo would be drawing more than it's rated to draw, due to an internal fault.
     
  19. ftl

    ftl Explicator

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    Running any high-power device from the 12V system without connecting it through a suitably-sized fuse is just asking for trouble.
     
  20. GregP507

    GregP507 Senior Member

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    And that lends even less credibility to the theory that the DC-DC converter may not be "keeping-up" to the stereo. Basically, the idea is wrong.
     
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